Preventing color fog in photographic material



July 9; 1946. E. E. JELL EY ETAL 2,403,721

PREVENTING COLOR FOG IN PHOTOGRAPHIC MATERIAL Filed Sept. 23, 1943 EABLE LAYER CONTAINING REDUCING AGENT Yl ELLOW FILTER EMULSION LAYERS CONTAINING COUPLERS SUPPORT EDWIN E. JELLEY PAUL W. VITTUM INVENTORS Wflm 6a \7 ATTORNEYS Patented July 9,- 1946 7.

PREVENTING COLOR FOG IN PHOTO- GRAPHIC MATERIAL Edwin E. J elley and Paul W. Vittum, Rochester,

N. Y., assignors to Eastman Kodak Company, v Rochester, N.'Y., acorporation of New Jersey "Application septe ber 23, 1943, Serial No. 503,472

Claims. (.01. 95-8) This invention relates to color photography and particularly to amethod for preventing the formation of color fog 0r stain in photographic emulsions containing couplers.

The method of color photography in which color-forming or coupling compounds combine with the development product of aromatic amino photographic developers to produce dyes is Well known. The color formers or couplers used in' this method may be added directly to the sensi tive emulsion layers as described in Fischer U." S.

Patent 1,102,028, granted June 30, 1914, or may be incorporated in a water-permeable medium which is insoluble in the colloidal carrier 'for the sensitive silver salt as described in Mannes & Godowsky U. S. Patent 2,304,940,,granted December 15, 1942,01 our U. '8. Patent 2,322,027, granted June 15, 1943. I

' A difliculty' frequently -encounteredin "these processes is the formation of color fog or stain. When the exposed material is developed in a color-forming developer, dye fog is frequently formed in the emulsion layer. This is because the developing agenthas been oxidized to some exte'ntby the action'of ,thejair and the oxidized developer'tendsfto couple with the color-forming compound'at places'in the photographic material where no' silver image is produced. It is Well knownthat in thes'e'processes'thedye shouldbe formed only where the silver halide "is reducedto metallic silver, thereby oxidizing the developing agent toa form'which coupleswith the 70010; former. Once the developing agent is oxidizei'it couples immediately'with'the color former whethl' er a photographic image is present or not. Aerial oxidation of' the developer oroxidation by means other than the photographic image therefore con verts the developer to a form which will immedi atelyreact with thecolor' formert'o' produce a colorfog or stain. This efiect is especially no:

2 reducing agent capable .of reacting with the oxidized developer in the developing solution to yield substantially colorless products. The oxidized developer present in the developing solution is thereby prevented from reaching the sensitive layers containing couplers and combining with the couplers where the layer was not exposed. The unoxidized developing agent can penetrate through the layer containing the reducing agent unaffected, and develop the exposed portions of the emulsion layer or layers to form colored images therein. V

In the accompanying drawing the single figure is a sectional view of a film constructed according to our invention. In

The water-permeable layer containing the reducing agent used according to our invention is coated over the sensitive-emulsion layer of the photographic material. The overcoating layer may be used with single layer photographic materials althoughit'is ofgreater value with multilayer materials containing couplers in one or more of the sensitive emulsion layers such as those described in the Mannes & Godowsky U. S.

Patent 2,304,940 or our ;U.. s. Patent 2,322,027,

referred to above. Thesensitive material may be film or paper and mayhave a transparent or an opaque base. I

In the case of a film material, the efiect of the extra layer containingthe reducing agent is to render the developer difiusing through it substantially free, from oxidation products which would otherwise -.cause'color fog. With paper materials, most of the difiusion takes place through the emulsion side so; that the overcoating'layer is usually adequate for preventing stain. However, there might be'a slight gain in freedom from color iog in the lowermost sensitive layer of a paper coating if a layer were placed between ticeable' in materials having couplers'incorporated in thesensitive emulsion'layer since there is no coupler in the developing solution to react with any developing agent which-is oxidizedby the action of the air. Fog or stain arising from these causes is not readily centrolledby the same procedures used to controlsilver fog. f 4

c It is an object of the presentyinvention to prevent that particular type ,of color fog which is caused by the oxidized developer penetrating the upper layers of a multilayer photographic material containingcouplers, A fu-rther'objectis to provide a sensitive photographic materialcon:

taining couplers 'and provided with an overcoating layenwhich'affords protection against such: V V y r These objects are accomplished, according to our inventi n',"by providing overfthe' multilayer material .a layer of a ,water p'ermeable "colloidal material containing a substantially non-diffusing it and the paper base containing a substantially non-difiusing reducing agent capable of destroying developer oxidation products.

The overcoating layer used according to our invention may consist of any suitable water-permeable colloidal material such as gelatin, collodion or other cellulose ester or synthetic resin such as polyvinyl alcohol. 4 "A suitable amount of a reducing agent is added to the colloidal material which is coated as a layer on the finished film. The reducing'agent'should be non-difiusing in the layer in which it is'incorporated so that it does not contaminate the adjacent sensitive emulsion layer. We prefer to use an organic reducing agent containing an aliphatic group having a carbon chain of at least 8 carbon atoms, such as a higher'fattyacid residue. Hydroquinones having long chain aliphatic groups are especiallysuitable although wemay also use 3 The following compounds, which are by way of example only, are suitable for use according to our invention:

n-Octyl hydroqulnone on Ca la-Q0631" n Di-n-octyl hydroquinone I QCHHH n-Dodecyl hydroquinone Dl-n-dodecyl hydroquinone OctadecyI hydroquinone CmHns Chloro-n-dodeoyl hydroquinone on 7 Q0 020mm, H

Lauryl gentisate on ONHC 0 cum: I

2-lauroylamino-4-aminophenol p-lllaurylphenylhydrazine 2,403,721 if M 3 of incorporating the reducing agent will be explained by reference to the following examples.

Example 1 A solution of 2 grams of didodecyl hydroquinone in a mixture of 130 cc. of 95% ethyl alcohol and 10 cc. of 20% sodium hydroxide solution was added to 1000 cc. of melted 5% gelatin solution. To this solution there was added sufficient citric acid solution to bring the pH to the desired value, for example, about pH 6.5. The mixture was then coated on a multilayer material containing couplers.

Example 2 A solution containing 4.5 grams of p-lauryl phenyl hydrazine and 10 grams of n-butylphthalate in 200 cc. of ethyl acetate was emulsified with 400' cc. of 0.5% aqueous solution of triisopropyl naphthalene sulfonate. The emulsification was effected by passing the mixture several times through a colloid mill. The resulting emulsion was subjected to heating on a steam bath with constant stirring to dissolve, off the ethyl acetate and the remaining water suspension was added to 500 cc. of melted 10% gelatin. mixture was diluted with water to one liter and was then coated on a multilayer material containing coupiers.

Our invention will now be described by reference to the accompanying drawing.

As shown in the drawing, which is a sectional view of a film constructed according to our in vention, I0 is a support of cellulose ester or other suitable material having thereon gelatino-silver halide emulsion layers ll, l2 and I3 sensitive, respectively, to the red, green and blue regions of the spectrum. Emulsion layer. 1 l contains a coupler capable of producing a cyan dye image upon development, emulsion layer I2 containsv a coupler capable of producing a magenta dye image upondevelopment, and emulsion layer l3 contains a coupler capable of producing a yellow dye image upon'development. Suitable couplers are described in Mannes 8: Godowsky U. S. Patent 2,304,940 or our U. S. Patent 2,322,027. The usual yellowfilter layer H1 is employed between layers l2 and I3 to prevent action of blue light on the layers It and I2; Overv the layer l3 there is a gelatin layer [5 containing a reducing agent which is non-diffusing in the gelatin.

In our process the reducing agent is located in its own separate layer away from thesensitive silver halide. For this reason, together with the fact that the reducing agent is substantially nondifiusing, agents may be used which could not be added to an emulsion layer because of fogging, desensitizing or interfering with normal dyeimage formation. r

The reducing power ofthe reducing agents used, according to our invention, may be determined by reference to their action on a solution of ammoniacal silver nitrate. A solution of ammoniacal silver nitrate is prepared by making a normal solution of silver nitrate and adding to it a 28% solution of ammonium hydroxide slowly until the first formed precipitate just dissolves. The compound to be tested for determiningits suitability for use in our invention i said emulsion layer an outermost, exposed layer of a water-permeable colloid containin an organic reducing agent for oxidized photographic developers, said reducing agent containing an aliphatic group having a carbon chain of at least 8 carbon atoms and being non-diffusing in said water-permeable colloid layer.

2. A multilayer photographic fihn comprising a support having thereon at least one silver halide emulsion layer containing a coupler, and over said emulsion layer a layer of a water-permeable colloid containing a hydroquinone having attached thereto a substituent group rendering said hydroquinone non-difiusing in said water-permeable colloid layer. l

3. A multilayer photographic film comprising a support having thereon at least one silver halide emulsion layer containing a coupler, and over said emulsion layer a layer of a Water-permeable colloid containing a hydroquinone having therein an aliphatic group having a carbon chain of at least 8 carbon atoms.

4. A multilayer photographic film comprising a support having thereon at least one gelatinosilver halide emulsion layer containing a coupler, andover'said emulsion layer a layer of gelatin containing a hydroquinone having therein an aliphatic group having a carbon chain of at least 8 carbon atoms.

and over said emulsion layer a layer of gelatin containing a hydroquinone substituted with an alkyl radical having a carbon chain of at least 8 carbon atoms.

EDWIN E. JEILEY.

PAUL W. VITTUM. 

